Raisins in a Hydrogen Pie: Ultrastable Cesium and Rubidium Polyhydrides

Abstract

We proposed a new method for synthesis of metal polyhydrides via high-pressure thermal decomposition of corresponding amidoboranes in diamond anvil cells. Within this approach, we synthesized molecular semiconducting cesium ($\text{P}4/nmm$-CsH${}_7$, $\text{P}$1-CsH${}_{15+x}$) and rubidium (RbH${}_{9-x}$) polyhydrides with a very high hydrogen content reaching 93 at%. Preservation of CsH${}_7$ at near ambient conditions, confirmed both experimentally and theoretically, represents a significant advance in the stabilization of hydrogen-rich compounds. In addition, we synthesized two crystal modifications of RbH${}_{9-x}$ with pseudo hexagonal and pseudo tetragonal structures identified by synchrotron X-ray diffraction and Raman measurements. Both phases are stable at 8-10 GPa. This is an unprecedented low stabilization pressure for polyhydrides. These discoveries open up possibilities for modifying existing hydrogen storage materials to increase their efficiency.

References in corpus (2)

• Rubidium Polyhydrides Under Pressure: Emergence of the Linear H3- Anion
• High-temperature superconductivity in hydrides